1. Field of the Invention
The present invention relates to a brake control apparatus for a bicycle, and more particularly to a brake control apparatus having a control lever and a cable operatively connected to the lever to be pulled thereby.
2. Description of the Related Art
With a typical conventional brake control apparatus of the above-noted type, the control lever is pivotably supported to a bracket and the control cable is fitted into a hole formed at the root end of the control lever. Accordingly, the connecting portion of the control cable relative to the lever is maintained fixed relative to the pivot of the control lever (e.g. Japanese published utility model gazette No. 57-9193).
For fully understanding the sprits of the present invention, it should be helpful to define and explain here some essential concepts on which the invention is based.
First, a cable movement ratio is defined here as a ratio obtained by dividing an output force of and along the cable associated with application of a unit input force to a certain position of the control lever by said unit input force.
Second, considering the possibility that the input force applied to the lever substantially equates with the amount of work transmitted to the cable; then, a cable movement ratio is defined here as a ratio which varies in inverse proportion to the above force transmission ratio. That is to say, this cable movement ratio is obtained by dividing an amount of movement of the lever associated with a unit operation amount of the lover at a certain position thereof by said unit lever operation amount. These cable movement ratio and the force transmission ratio are predetermined by the construction of the brake control apparatus per se and are not directly affected by elastic modulus of the brake shoe and/or of the cable.
Then, during an initial stroke of the lever where this force transmission ratio has a relatively small value, even if a considerably large unit input force is applied to the lever. That is, even if the control lever is pulled with a considerably large manual force, the cable output force remains relatively smell thus being unable to bring the brake shoes into sufficiently effective pressure contact with the rim of a bicycle wheel. On the other hand, if the same amount of input force is applied in the subsequent stroke, the cable output force will be excessive thus too quickly establishing the pressure contact between the shoes and the rim.
In connection with this problem, according to the conventional apparatus, however, the distance between the pivot of the control lever and the connecting portion of the cable remains fixed throughout the operational stroke of the lever; that is, the force transmission ratio remains fixed regardless of the lever position subjected to the input force. Further, with the convention, the cable is connected with the lever so that within the limited entire stroke of the control lever the force transmission ratio has the minimum value during the braking stroke of the lever where the contact between the shoes and the rim is established. Therefore, it is impossible to maintain the force transmission ratio relatively high through the braking stroke of the lever. In short, even a relatively large amount of lever movement can often fail to provide sufficient braking force. In addition, since even a small amount of lever movement results in a large amount of movement of the shoes, a fine braking action has been very difficult.
Accordingly. the primary object of the present invention is to provide an improved brake control apparatus which can apply a strong braking force even with a small input force and which makes a fine braking action readily possible.